1. Field of the Invention
The present invention relates to the separation and recovery of gallium values, by liquid/liquid extraction, from highly basic aqueous solutions containing such gallium values, for example the sodium aluminate liquors emanating from the Bayer process for the production of alumina.
2. Description of the Prior Art
Processes are known to this art for the recovery of gallium values present in aqueous alkaline solutions by liquid/liquid extraction utilizing an organic phase containing an extractant and an organic solvent, as well as for the purification of the gallium solution to eliminate certain cations, such as, for example, the aluminum and sodium cations extracted together with the gallium values from the aforesaid aluminate liquors. Particularly compare published French Applications Nos. 2,277,897, 2,307,047, 2,307,882, 2,495,601, 2,532,295 and 2,532,296.
Such processes entail transferring the gallium values contained in the strongly basic solution into the organic extraction phase by a liquid/liquid extraction technique. In a second stage, this organic phase is treated with an acid solution to back-extract the gallium, with aluminum and sodium cations also being extracted.
The acidic gallium solution containing aluminum and sodium ions is then treated separately to separate the gallium values and the metallic ions.
Numerous processes have been proposed to the art for such purpose and, in particular, the processes described in published French Applications Nos. 2,495,599, 2,495,600 and 2,495,601, assigned to the assignee hereof.
These processes comprise either treating the gallium solution by cascading same over an ion exchange resin of strongly basic type, or extracting the gallium by liquid/liquid extraction, with the extractants being quaternary ammonium salts or alcohols, for example.
The gallium solution may then be subjected to new purification stages.
The final gallium solution is then treated by different processes to produce gallium metal of very high purity, or alloys of gallium with other compounds.
The aforedescribed processing makes it possible to obtain, in very good yields of extraction and recovery, a gallium solution of very high purity. However, the second stage of the process, i.e., the treatment of the organic phase with an acid solution, requires the consumption of a large amount of the acid solution, which is discharged as an effluent after use. These significant liquid effluents are disadvantageous, as they require treatment prior to their discharge, thereby increasing the overall cost of the process.